Stanley McChrystal, former commander of coalition forces in Afghanistan, says the U.S. and its NATO allies are only “a little better than” halfway to achieving their military goals, partly due to a “frighteningly simplistic” understanding of the country.

In remarks at the Council on Foreign Relations, McChrystal said on Thursday that the biggest problem facing the U.S. will be to create a stable, legitimate Afghan government that can serve as a counterbalance to the Taliban.

Friday marks the tenth anniversary of the invasion of Afghanistan in 2001. Over the past decade, more than 2,500 international troops have been killed, including nearly 1,800 American troops in the ongoing “Operation Enduring Freedom.”

McChrystal pointed out that coalition forces have lacked — and still lack a solid comprehension of Afghanistan’s situation, culture and history, and made the bleak assessment that the work is only about half done.

“We didn’t know enough, and we still don’t know enough,” he said at the Council on Foreign Relations, reports the BBC. “Most of us — me included — had a very superficial understanding of the situation and history, and we had a frighteningly simplistic view of recent history, the last 50 years.”

The retired four-star general said that U.S. forces did not know the country’s languages and did not make “an effective effort” to learn them.

The invasion of Iraq put a strain on military resources, McChrystal said, and also changed the way the Muslim world viewed America’s foreign policies.

“When we went after the Taliban in Afghanistan in 2001, there was a certain understanding that we had the ability and the right to defend ourselves and the fact that Al Qaeda had been harbored by the Taliban was legitimate. I think when we made the decision to go into Iraq, that was less legitimate” in view of the Muslim world, McChrystal said.

McChrystal resigned his post as commander of coalition forces in Afghanistan in 2010 after a magazine profile quoted him as being critical of Obama administration officials. He retired from the Army shortly after.

President Barack Obama and the First Lady marked the 10th anniversary with a statement from the White House.

“As we mark a decade of sacrifice, Michelle and I join all Americans in saluting the more than half a million men and women who have served bravely in Afghanistan to keep our country safe, including our resilient wounded warriors who carry the scars of war, seen and unseen,” said Obama in a statement. “Thanks to the extraordinary service of these Americans, our citizens are safer and our nation is more secure… And as we reflect on ten years of war and look ahead to a future of peace, Michelle and I call upon all Americans to show our gratitude and support for our fellow citizens who risk their lives so that we can enjoy the blessings of freedom and security.”